3Com 7600 manual Illustrates the VCCs active among LAN Emulation Components

12-8CHAPTER 12: ATM, LAN EMULATION, AND VIRTUAL LANS

LEC Control Frame The operator can display statistics on the various types of control frames Statistics Display in and out of the LEC (see “Display LEC Control-frame Statistics” on page

8-14)

Data VCCs Data VCCs carry data frames between LECs and between a LEC and the BUS. Unicast data is normally sent from one LEC to another LEC by data-directVCCs. Data direct VCCs are set up dynamically in a SVC environment by a transmitting LEC after ascertaining the ATM LEC destination address for the packet to be transmitted. Once established, a data-direct VCC remains in place for transmission of subsequent traffic between the two LECs. However, a data direct VCC that remains unused for VCC-Timeout-periodis released by the LEC.

Amulticast data VCC pair (multicast-sendand multicast-forward) are established between a LEC and the BUS in order to allow the LEC to send and receive multicast data. In addition, initial unicast data (data whose LEC destination has not yet been ascertained by the transmitting LEC) is sent on the multicast-send VCC to the BUS which forwards it to all other LECs in the same ELAN. Characteristics of the data VCCs are summarized in the following table:

Table 12-2 Data VCCs

VCC Name	From/To	Information carried	Initialized by	Duration
Data-direct	LEC<==>LEC	Point-to-point Unicast data	LEC	Established by
		between LECs		need and released
				when unused for
				VCC-Timeout-
				period.
Multicast-send	LEC<==>BUS	LEC sends multicast and	LEC	Membership of
		initial unicast data to BUS		LEC in ELAN.
Multicast-forward	BUS==>LEC	BUS distributes data traffic to	BUS	Membership of
		LECs		LEC in ELAN.

Figure 12-1 illustrates the VCCs active among LAN Emulation Components.